Saturday, 18 June 2016

Biomechanics of the Rowing Stroke by Narelle Badenoch & Amaya Walling

The Question

What considerations must be implemented and considered when perfecting the rowing stroke? Understanding the biological system of the rower, as well as the design of the mechanical system, the boat, and the motion dynamics of rowing, is vital in order to achieve maximum boat velocity being applied to a quadscull within rowing (Baudouin, A & Hawkins, D 2002). The following discusses what biomechanical aspects influence a rowing stroke, as well as how this can be used to achieve optimal, efficient technique.

The Answer

Rowing Technique and Sequence:
In order to understand how the rowing techniques can be improved, we must understand the stroke phases essential to optimal technique. The break down of the rowing technique begins with the grip, followed through to the catch, drive, release and recovery.
The grip consists of the drive grip and the recovery grip. During the drive stroke, the handle should be gripped with a flat wrist with the knuckles at the base of the fingers in the middle of the handle. The fingers then roll out during the recovery then squaring up once positioning at the catch. A relaxed grip is used and the handle should not be held too firm at the end of the handle with the thumbs on the end of the grip in sculling and during the sweep, the outside hand at the end of the handle with the inside hand towards the blue grip. The left hand should lead the right hand during the recovery phase. During the drive, the hands should not change from the recovery that is the right hand leading ahead of the left (Nolte, n.d; Kleshnev, 2010).

During the catch (the start of the drive phase), shins must be vertical with the lower back tucked in sitting up slightly. Due to body differences that we must consider (i.e. shorter rowers and taller rowers) variables such as: more body length, less shin angle, etc. small variations may change to this phase. The head must be straight with relaxed shoulders. Blades are placed in the water and the boat is driven forward using the large muscle groups in the legs and body (see figure 1). The body should be leaning forward and the body close to the thighs. The hands are lifting upwards fully locking the blades in the water (Kleshnev, 2010).

During the drive phase beginners may often feel, as though the arms are doing majority of the work, however, this is not the case. Primarily the larger leg muscles will be in action with the arms more relaxed with hands parallel to the boat. Towards the end of the drive, the body (back) swings back and the arms are then used to maintain momentum of the blade handles allowing for continued acceleration of the blade through the water (Nolte, n.d).

During the release, the rower’s hands then make a small tap downwards lifting the blades away from the water. The legs should be flat down with their back straight however slightly leaning back creating a pull on the abdominal muscles. The blade handles brush the body when the spoon end is flat on the water. Blades are then feathered to become parallel to the water, which allows for a more aerodynamic position. The recovery phase then begins (Nolte, n.d).

The recovery phase begins with the hands moving down and away in an opposite sequence to the drive. The arms move away from the body vertically balanced, with the shoulders neck and arms relaxed. This posture ensures recovery from the exertion of the stroke and aids in keeping the boat balanced in the water. The body then rocks on from the pelvis with straight back and lifted knees allowing the seat to move (Nolte, n.d).
Figure 1: Muscles used during the catch, drive, release (finish) and recovery (Mazzone, 1988). 







Newton’s laws of motion:

There are three Newton’s laws of motion, all of which can be applied to a rowing stroke.

Newton’s first Law of motion describes “Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon” (Kuehn, K 2015). Newton’s second law of motion states that “the alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed” (Kuehn, K 2015).  Newton’s third law of motion states “to every action there is always opposed to an equal reaction; or in the mutual actions of two bodies upon each other are always equal, and directed to contrary parts” (Kuehn, K 2015). In relation to rowing, in order to move a boat faster, its needs to overcome the inertia of the boat against the water (1st Law), by having a force applied against it (2nd law). To do this a large and direct force needs to be applied against the water, which ultimately applies an equal and opposite reaction force against the boat (3rd law). As the sum of forces dictates our acceleration of the boat and the force of gravity acts against it (Newton’s Law of Gravitation), it is important to produce large horizontal forces in order to propel the boat forwards. Downward forces need to also be applied to lift the boat out of the water, whilst also maximising horizontal force production (Blazevich, A 2010).

Impulse-momentum relationship and momentum:

A boat is propelled through the water by the use of various muscle groups, which ultimately produce a force which is then transferred to the water by the oars, which are then free to rotate around a vertical axis (Caplan, N & Gardner, T 2007).  During the drive phase, the force applied is inconsistent, due to the various muscle sizes and groups used throughout the stroke. The ground reaction forces also vary throughout the stroke. When a rower is positioned at the catch, blades in the water and the balls of the feet in contact with the footplate, the force is then predominately generated using the Gluteus Maximus and Quadriceps muscles. Force is applied to the handles, and during the push phase all joints in the kinetic chain move simultaneously in a single movement (Magias, T 2016).

This part of the rowing stroke is referred to as the “impact peak”, due to being the initiator of power production (Blazevich, A 2010). As the rower moves through the stroke, the force is directed from the ball of the foot to the heal of the foot, as the legs begin to fully extend. Once the legs are fully extended, the torso begins to open up, at the hips, and as the boat continues to accelerate through the water, the arms begin to pull the handles of the oars towards the chest, until the body is in line with the hips, at a degree of 100-105˚, in relation to the torso to the femur (Korner, T 2016). This stage of the drive sequence is referred to as the “finish” and is the “propulsive peak” of the stroke as maximum propulsion is achieved. Separating the rowing stroke into a sequence promotes optimal length as the body is fully contracted at the catch, and separating the drive sequence, provides optimal boat speed (Magias, T 2016). Following this the rower then returns back to the catch, through the recovery sequence (Blazevich, A 2010).

If we want to increase the speed of the boat of a constant mass, we need to increase the velocity and therefore momentum of the boat. To increase the boats momentum, a greater amount of force needs to be applied. Therefore, when a rower is positioned at the catch, with the blades positioned in the water, the largest amount of force possible needs to be applied for the longest time possible in order to produce maximum momentum; the greater the impulse, the greater the change in momentum due to change in mass and in turn change in velocity. This is referred to as the “impulse-momentum” relationship. Therefore the muscle groups used throughout a rowing stroke need to exert a greater deal of power or force. Long rowing strokes are also required in order to increase the time available for the force to be applied, and to essentially increase the impulse of the stroke. (Blazevich, A 2010).

Extra acceleration comes from the recoiling of elastics tissues, such as tendons, which are stretched when the legs are compressed by vertical and breaking forces, when sitting at the catch with the shoulders over the hips. Whilst breaking force is intended to be minimised, nonetheless a small amount of breaking force is required in order for the blades to effectively connect at the beginning of a stroke, at the catch. This is particularly important, when rowing at high speeds, which require a higher stroke rate, to ensure that maximum connection is achieved, when fully compressed at the catch (Blazevich, A 2010).

Torque and centre of mass:

The force applied to the oar handle, and also movement, is affected by the joint strength and torque velocity of the rower. In order to maximise power, which is sustainable, the rigging set-up and blade design are to be matched to the rower’s joint torque-velocity characteristics. Coordination and timing are key contributors in regards to overall system velocity (Baudouin, A & Hawkins, D 2002). When force is applied to the foot plate, to accelerate the boat, the boat attains horizontal velocity, with the movement of the boat being represented by the centre of gravity. It is relatively difficult to balance a rowing boat; therefore part of this requires the manipulation of body parts to ultimately find the centre of mass, to therefore achieve balance. The body’s centre of mass within the boat lies within the base of support, between two level hand heights when sitting at the catch. If the centre of mass moves outside the base of support, either by moving the knees in one direction or having unequal handle heights (determined by blade height of the water), this essentially minimises the base of support, and ultimately balance is not achieved (Blazevich, A 2010).

Angular Kinetics:

To return the body back to the catch, from the finish position, we need to overcome inertia. As the torso swings over at the hips, moment of inertia is applied. Moment of inertia describes the propensity for masses, which are at a distance from the centre of rotation, to resist changes in their state of motion. As the boat is moving in a straight line, mass and inertia are similar. The change in oar length and weight can ultimately determine the inertia of the oar. Increasing the length of the oar reduces the distance from the hands, when sitting at the catch, and ultimately the centre of rotation to the main mass of the oar, essentially reducing the oars moment of inertia. Reducing the length of the oar, allows for increased length forward, into the catch, essentially allowing for maximised boat connection (Blazevich, A 2010).

Muscle force and joint movements depends greatly on the velocity of the movement. As joint velocity increases, muscle torque produced about the joints decrease. Effort level ultimately determines the optimal angular velocities for power production.  Stroke rate and rigging set-up can also determine angular velocities, through examining a rower’s joint torque-velocity and torque-angle profiles. This therefore allows for power delivery to be increased through lever action of the oar in order to provide maximum sustainable power throughout the stroke (Baudouin, A & Hawkins, D 2002).

Angular acceleration of an object will be greater if torque is increased or the moment of inertia is decreased. In a rowing stroke, force is applied at the hip joint through the Gluteus Maximus and quadriceps muscles, essentially this is torque. The “moment arm” refers to the distance between the muscle and the joint centre.

The greater this is, the more torque which can be generated about the hip joint (see figure 2) for a given lever of muscle force. Moment arm can evidently not be changed through training; muscle forces however can be improved. Within rowing, increasing torque essentially increases angular velocity of the leg and therefore the speed at which the foot comes in full contact with the foot plate. Full contact of the feet to the foot plate is optimal as surface area is increased, and maximum force can be produced (Blazevich, A 2010).
Figure 2: Hip Angle



Work, power and energy:

The amount of work or energy supplied during a single rowing stroke is equal to the average force that is applied, multiplied by the distance of which the boat moves (Blazevich, A 2010). To increase power results in an increase in boat velocity, however a single rowing stroke can be relatively draining in terms of energy. Therefore mechanical energy and metabolic energy are two factors which are taken into consideration in order to perform a great deal of work with little energy cost. Mechanical energy, in relation to rowing, refers to the energy which is associated with a boats movement, kinetic energy, or its position, potential energy. An increase in velocity, results in an increase in kinetic energy; the more power which is produced, the greater the velocity, and the greater the kinetic energy which is produced as a result. 

To improve rowing efficiency, kinetic energy (output) needs to be increased, and the energy required (input) to move the boat needs to be decreased. To ultimately improve the efficiency of a rowing stroke, technique can be changed, however this varies depending on the individual and their body type and composition. Efficiency can also be improved through physical training. An individual can improve their physical fitness in order to perform and train harder for longer. The ultimate aim for a rower is to increase power output whilst also improving and maintaining efficiency (Magias, T 2016).

Gravity, buoyancy, drag and propulsion:

There are four forces that act on a boat throughout a rowing stroke, these include: gravitational, buoyant, drag, and propulsive.

Figure 3: The four forces acting on a boat shell (Baudouin & Hawkins, 2002).
In the horizontal direction, propulsion and drag are the two acting forces (Baudouin, A & Hawkins, D 2002). Drag is a force, which resists motion, and propulsion assists with motion. Based on Newton’s 3rd Law, action-reaction, to propel the boat forwards, a backward force must also be applied. Reaction power is not equal and opposite to that of action power in rowing. This is because water is not a solid, and therefore it moves when force is applied. Therefore not all power which is applied, is not used to propel the boat forwards, some is used to induce movement in the water, as the blade enters the water (Blazevich, A 2010). In order for efficient rowing technique to be applied, in terms of blade entry, the blade must enter and make connection with the water ¾ up the slide, during the recovery phase. The blade enters the water at the maximum point of reach during the catch phase in order to take the drive directly up without “missing water” and disturbing the boat force. This will then result in a late catch shorter effective stroke causing less acceleration developed resulting a lower boat speed.

Hydrodynamic drag is created during a rowing stroke, and consists of three drag quantities; skin, form and wave drag. This is a force that occurs when the boat moves through the water at the interface of air and water with different densities. The wave essentially applies an opposing force against the boat, and in turn the turbulence, which is created ultimately, slows down boat velocity, as well as increases the energy required to row at a given speed. Drag is ultimately affected by frontal surface area and the shape of the boat (Blazevich, A. 2010).  

The faster the boats speed, the greater the drag (Blazevich, A. 2010). Blade force is the only form of propulsive force to counter both air drag and hydrodynamic drag (Baudouin, A & Hawkins, D 2002). Propulsive forces are applied in order to overcome the water resistance placed on the shell of the boat, as well as the air drag being applied to the rower and the oars. This essentially applies to Newton’s second law of motion (Caplan, N & Gardner, T 2007). Research suggests that in order to reduce the impacts of drag, technique is a contributing factor in order to provide efficiency. Boat size and weight is also a determining factor that determines the size and effect of drag (Blazevich, A 2010). In the vertical direction, buoyancy and gravity are acting on the combined mass of the boat, the rower, and the oar, in order to achieve equilibrium (Baudouin, A & Hawkins, D 2002). In rowing, the underbellies of the boats are designed in order to provide optimal lift, and minimal drag. Evidently, the heavier the boat, and crew members, the lower the boats sits in the water, creating more drag, and in essence; the lighter the boat, and the crew, the less drag created (Blazevich, A 2010). There is however a mandatory boat weight for a quad in rowing competitions of 52kg (New South Wales, 2004).

Kinetic chain:

A push-like movement pattern is used during the drive phase, where all joints in the kinetic chain extend simultaneously. As the legs drive back, extension at the knees, and torso in an upright position, shoulders are locked over the hips. The accumulation of forces generated around each joint, results in an overall production of force. A push-like pattern can be used to improve force production and accuracy (Magias, T 2016).

Kinetic energy is supported during the drive phase, and is lost during the recovery phase. The average kinetic energy of rowers is much higher than that of the boats energy. The gain of energy during the drive phase is much higher for the rower, compared to the boat. The rower accumulates 82-90% of the systems kinetic energy, compared to the boat which acquires 10-18%. During the recovery phase, the boat shell receives nearly the same amount of energy from that of the rower during the drive phase. This exchange of energy however, between the boat and the rower, does not affect acceleration of the whole system (Kleshnev, V., 2002). During the catch phase, the rower’s acceleration is higher than the acceleration of the boat itself and therefore uses the kinetic energy of the boat shell. This stops their recovery movement and allows their body mass to accelerate before the rower places the blade into the water. Rowers apply more ‘net propulsive force’ to the boat shell whilst at the same time, accelerating their body mass significantly increasing the speed of the whole rowers-boat system (Kleshnev, V. 2002).

Injury Prevention:

As clearly listed in figure 1. Rowing is a physically demanding sport on all aspects of the human body. This requires maximal body effort and proper flexibility. Due to the physiological demands on the muscular system, in order to prevent injury, appropriate strength conditioning and cardiovascular training programs in conjunction with a rowing regime will help to improve performance, decrease injury and aid in recovery (Rumball, Lebrun, Di Ciacca & Orlando, 2005 & Athletes Equation, 2014).

Due to excessive hyper flexion and twisting, the most frequently injured region is the low back. This can result in specific injuries such as spondylolysis, sacroiliac joint dysfunction and disc herniation (Rumball, Lebrun, Di Ciacca & Orlando, 2005). In order to strengthen the lower back, various strengthening workouts can be implemented. Exercises such as: hang power cleans, front squats, deadlifts, Romanian deadlifts (see figure 4), bent over rows and Russian twists should be considered to maximise back and core strength (Athletes Equation, 2014).
Figure 4: 


Conclusion:

The information as discussed allows an insight to the biomechanics involved with the rowing stroke in order to achieve optimal, efficient technique. In conclusion, in order to achieve this, the key elements of: techniques and sequence, newtons three laws of motion, impulse momentum relationship and momentum, torque and centre of mass, angular kinetics, work, power and energy, gravity, buoyancy, drag and propulsion and kinetic energy must all be considered and understood. As rowing is one of the most physically demanding sports, sufficient training must too be considered in order to maximise results and enhance performance.





References:

·       Athletes Equation. (2014). Strength Training for Rowers. Athletes Equation: The Solution for Elite Performance. Retrieved from: http://athletesequation.com/strength-training-for-rowers/

·      Baudouin, A., & Hawkins, D. (2002). A biomechanical review of factors affecting rowing performance. British journal of sports medicine, 36(6), 396-402.

·      Blazevich, A. (2010). Sports Biomechanics, the basics: Optimising human performance. A&C Black.

·      Caplan, N., & Gardner, T. (2007). A mathematical model of the oar blade–water interaction in rowing. Journal of sports sciences, 25(9), 1025-1034.

·      Ferguson, A. (2016). Rowing techniques for coaches: catch, drive, release and recovery. ACT Rowing Association. Retrieved from: http://rowingact.org.au/former%20website/SDO/TECHNIQUE_1.html

·      Kleshnev, V. (2010). Biomechanics for rowing technique and rigging. Bio Row. Retrieved from: http://www.veslo.cz/odborne-texty-ke-stazeni/5639914/Biomechanics_for_Rowing_technique_and_rigging_by_V._Kleshnev.pdf

·      Kleshnev, V. (2002). Moving the rowers: Biomechanical background.Australian Rowing, Carine, WA, 25, 16-19.

·      Korner, T. (2016). A comparative analysis of GDR and Adam Styles, accessed on 16/06/2016, from World Rowing: http://www.worldrowing.com/uploads/files/3Chapter2.pdf.

·      Kuehn, K. (2015). Newton’s Laws of Motion. In A Student's Guide Through the Great Physics Texts (pp. 261-264). Springer New York.

·      Magias, T. (2016). Workshop- Impulse- momentum relationships in Physical Education, in HLPE3531 workshop, on May 26th 2016, Flinders University, Bedford Park, SA.

·      Magias, T. (2016). Workshop- Energy, work, efficiency, in HLPE3531 workshop, on June 9th 2016, Flinders University, Bedford Park, SA.

·      New South Wales. (2016). New South Wales Union of Rowers- Competitive Rowing Boat Types, accessed on 16/06/2016, from http://www.nswrowers.com/boats.html.

·      Nolte, V. (n.d.) Introduction to the biomechanics of rowing. FISA Coaching Development Programme Course - Level III. Retrieved from: http://www.worldrowing.com/uploads/files/3Chapter3.pdf

·      Rumball, J. S., Lebrun, C. M., Di Ciacca, S. R., & Orlando, K. (2005). Rowing injuries. Sports medicine35(6), 537-555.

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